Abstract: This paper details the application of PXI-based virtual instrument technology in radar speed measurement and successfully develops a radar speed measurement data acquisition and processing terminal. Keywords: virtual instruments, radar speed measurement, PXI 1 Introduction Virtual instrument (VI) technology has created a new concept in instrumentation and ushered in a new era of measurement and control technology. The essence of virtual instrument technology is to fully utilize the latest computer technology to realize and expand the functions of traditional instruments. Relying on the ever-evolving computer technology, virtual instruments provide users with a space to unleash their talents and imagination, design their own instrument systems, and meet a variety of application requirements. Compared with traditional instruments, virtual instruments have unparalleled advantages. Users of virtual instruments can design and define their own functions to meet special needs. Unlike traditional instruments, the key to virtual instruments lies in software implementation, which allows for easy modification of the software to meet different testing needs. The PXI specification is a new open, modular instrument bus specification released by NI on September 1, 1997. PXI is fully compatible with CompactPCI. PXI supports higher mechanical, electrical, and software requirements in industrial instrumentation, data acquisition, and industrial automation applications. To better suit industrial applications, PXI expands upon the CompactPCI specification, defining a robust architecture for PCI hardware that provides excellent mechanical integrity and easy installation and removal. PXI products offer higher and more granular requirements for environmental performance testing in industrial environments, including vibration, shock, temperature, and humidity. PXI adds necessary testing environments and active cooling to the CompactPCI mechanical specifications. This simplifies system integration and ensures interoperability across multiple vendors. 2. Radar Speed ​​Measurement Speed ​​radar uses the Doppler effect to measure the speed of moving targets. When there is a relative velocity between the target and the radar, the carrier frequency of the received target echo signal undergoes a frequency shift relative to the carrier frequency of the transmitted signal, namely the Doppler frequency shift. Its value is: fd = 2vr/λ where: fd — Doppler frequency shift (Hz) vr — Relative velocity between radar and target (m/s) λ — Carrier wavelength When the target moves towards the radar, vr > 0, and the echo carrier frequency increases; conversely, vr < 0, and the echo carrier frequency decreases. As long as the radar can measure the Doppler frequency shift of the echo signal, it can calculate the relative velocity vr of the target. 3 Hardware Composition of Radar Speed ​​Measurement System Based on Virtual Instrument 3.1 System Hardware Composition Block Diagram [align=center] Figure 1 System Hardware Composition Block Diagram[/align] 3.1.1 Antenna and Control System The radar system used in this paper is a continuous wave Doppler radar with a shared transmitting and receiving antenna. The main function of the antenna and its control system is to transmit continuous single-frequency radio electromagnetic waves, track the target, receive the echo signal reflected by the target, isolate it through a circulator, and output a Doppler frequency shift signal after passing through a mixer. Then, the Doppler frequency shift signal is input to the PXI acquisition and processing system. The Doppler signal frequency range (speed measurement range) of the antenna system used in this system is: 2K～140K (30～2000m/s), the output voltage amplitude range is: ±10V, and the output signal bandwidth is: 0-200KHz. The trigger starter outputs a shaped pulse trigger signal. Its output level amplitude is: ±5V, and the signal width is in microseconds. 3.1.2 Data Acquisition Module In the field of data acquisition, various instrument companies have developed a variety of data acquisition modules. There are PC-DAQ data acquisition cards based on various PC buses, as well as various data acquisition modules based on VXI and PXI buses. However, among the three VI architectures—GPIB, PC-DAQ, and VXI—GPIB is essentially an extension and expansion of traditional instrument functions through a computer; PC-DAQ directly utilizes standard industrial computer buses, lacking the bus performance required by the instrument; and building a VXI system for the first time requires significant investment. PXI, a new type of modular instrument system, is formed by adding mature technical specifications and requirements to the PCI bus core technology. It meets the requirements of testing and measurement users by adding a trigger bus and reference clock for multi-board synchronization, a star trigger bus for precise timing, and a local bus for high-speed communication between adjacent modules. Data acquisition modules based on the PXI bus have a maximum synchronous acquisition frequency of 10MS/s and a data transfer rate of 132Mb/s, which can well meet all the requirements of existing testing projects. Here, we use NI's PXI…6115 data acquisition module. Its sampling frequency: synchronous acquisition up to 10MS/s (greater than 10 times the signal input frequency, far exceeding the sampling theorem); vertical accuracy: 12 bits; 3.1.3 The computer control module adopts the NI PXI-1000B chassis, with 8 PXI slots, and the zero-slot control module adopts the PXI-PCI833X. NI's PXI-PCI833X product, through the use of MXI-3 technology, allows ordinary PCs to directly control the PXI system through transparent hardware and software connections. Multiple PXI chassis can also be connected using PXI-8330 and PXI-8335 modules. MXI-3 uses standard PCI-PCI bridge technology and 1.5Gb/s high-speed serial port connection, introducing a faster and more convenient expansion method for PXI control. Copper cables or optical fibers are used to connect to the computer system. The computer system can also be connected to a network measurement and control system to achieve remote testing. 3.2 Software Composition In virtual instruments, once the basic hardware is determined, different functions can be implemented through different software. Software is crucial for virtual instruments. Therefore, improving software programming efficiency becomes a very real issue. In today's information age, the key to improving software programming efficiency is to adopt object-oriented programming techniques. The choice of programming software not only affects the overall performance and functionality of the system but also its development time and efficiency. We cannot use simple programming methods; we need to use virtual instrument software development platforms to develop our own engineering application software. Commonly used virtual instrument software development platforms include HP's VEE and NI's LabVIEW and LabWINDOWS/CVI. Among them, NI's LabVIEW is a practical graphical software programming platform. LabVIEW provides a large number of function libraries for users to directly call, from low-level VXI, GPIB, serial port, and data acquisition module hardware control programs to more than 600 instrument driver programs, from basic digital functions, string processing functions, data operation functions, and file I/O functions to advanced analysis libraries (including signal processing, window functions, filter design, linear algebra, probability theory and mathematical statistics, curve fitting, etc.), covering almost all the functions needed in instrument design. On the LabVIEW software development platform, and by selecting a specific application-specific development toolkit attached to the software platform, the test system is graphically programmed. This modular programming function facilitates multiple choices and convenient debugging. The software interface is an open, fully Chinese human-computer interaction interface. Parameter selection and setting are all on one interface, with multiple windows that can be selected at any time, avoiding the complex interface of the previous layered drop-down layout. At the same time, the system supports various methods of Chinese input, making it more flexible and convenient to use. The entire radar test system software is divided into four modules: system test parameter setting, data (Doppler signal) acquisition, data FFT processing, and data file management. Figure 2 System software composition block diagram 3.2.1 System test parameter setting module: This includes setting the task name, task number, test time, location, relevant meteorological data, target parameters, and antenna position coordinates for the test task. 3.2.2 Data Acquisition: Real-time data acquisition is performed. Test conditions and parameters (including antenna frequency, signal input range, etc.) are input, and settings are made for the data channel, trigger level pulse, sampling time (trigger acquisition, time end), sampling frequency, and sampling method. The data acquisition hardware module is driven. Simultaneously, it automatically waits for signal triggering and stores the original acquired Doppler signal from the antenna output and related parameter information. [align=center] Figure 3 Data Acquisition Module[/align] 3.2.3 Data Processing: 3.2.3.1 Window Function and FFT Spectral Analysis: During the transformation of discrete signals using FFT operations, a "spectral leakage" phenomenon can occur. Windowing is used to reduce the impact of "spectral leakage." Choosing a suitable window function for a specific signal is not easy. The wider the window function, the stronger the clutter suppression capability; the narrower the window, the higher the resolution. This software provides several carefully selected commonly used window functions. The acquired raw Doppler signal is processed using FFT. The appropriate FFT operation data segment length (arbitrary input) and the number of FFT operation points (or velocity measurement points) can be arbitrarily input. The processed waterfall plot is displayed, and special bandpass digital filtering (significant effect) and FFT smoothing operations can be performed on the waterfall plot to filter out clutter noise interference. The filtered and smoothed power spectrum waterfall plot is then displayed. [align=center] Figure 4 FFT Spectrum Analysis[/align] 3.2.3.2 Velocity Calculation The frequency points of the acquired data are calculated using FFT, and waveforms (power waterfall plot, time-domain signal amplitude plot) are displayed. ZOOM functionality and cursor/mouse search functions are provided. Abnormal data can be removed, data smoothing performed, power spectrum analysis performed, amplitude spectrum analysis performed, and peak frequency points calculated and printed out. The processed target "velocity-time curve" is calculated and displayed using the formula vr=λfd/2, showing the target's initial velocity and radial velocity time data waveforms. The initial velocity is calculated, corrected, and the processed velocity result is displayed using the G. Math math library and the linear least squares fitting method provided by HIQ. [align=center]Figure 5 Velocity Calculation[/align] 3.2.3 Data File Management: Each test corresponds to a data file. When viewing, simply retrieve the corresponding filename. For each set of data, you can freely choose to print the original Doppler signal time-domain curve, the processed power waterfall curve, the processed VR-T curve, and the VR-T data. Each set of velocity data can be created into a file, and after necessary group processing, it can be printed out according to the specified table. 4 Conclusion Radar testing technology based on virtual instruments has broad application prospects in the field of microwave measurement. Through the development of a radar velocity testing system based on the PXI platform on the LabVIEW platform, we have gained a deeper understanding of the content, methods, and advantages of radar measurement technology based on virtual instruments. The virtual instrument we developed makes full use of existing technical resources, has rich system functions, flexible conversion, and a high performance-price ratio, achieving good results in practice. References: 1. *Radar Principles*, Ding Lufei and Geng Fulu, Xi'an University of Electronic Science and Technology Press. 2. *G Programming Reference Manual National Instruments*. 3. *Data Acquisition Basics Manual National Instruments*. 4. *Function and VI Reference Manual National Instruments*. 5. *Virtual Instrument New Products and Technologies*, Shaanxi Haitai. 6. *Doppler Radar Seeker Signal Processing Technology*, Gao Feng, National Defense Industry Press. 7. *Application of Digital Technology in Radar*, Dai Shusun, National Defense Industry Press. 8. *The PXI System Architecture National Instruments*.